The present invention relates generally to the field of automated analytical instruments and, more particularly, to a system of sample handling for automated clinical chemistry analyzers.
The Astra.RTM. System and the E4A.TM. Analyzer (available from Beckman Instruments, Inc., Brea, California) are clinical chemistry analyzers that illustrate two different types of analytical methodologies each having certain desirable attributes and advantages. The Astra Analyzer may include a plurality of individual analysis modules each having an open reaction cup. An automated sample probe withdraws a sample volume from samples carried on a carousel and distributes the sample volume to the analysis modules in accordance with the tests selected by the instrument operator.
The E4A Analyzer, on the other hand, utilizes a flow cell through which sample and diluent flow for the determination of four "electrolytes", namely, sodium, potassium, chloride and CO.sub.2. The analyzer includes a shear valve (disclosed in U.S. Pat. No. 4,297,903) having a bottom portion that swings to the side, allowing a sample pickup probe to extend vertically through the shear valve to aspirate sample from a cup aligned with the probe. The tip of the probe is withdrawn into the shear valve and the lower portion of the valve closes. Diluent from a diluent source flows into the valve, is mixed with the sample from the probe and flows to a flow analysis module.
The Astra Analyzer modules and the E4A Analyzer flow technology each provide unique advantages in the analysis of patient samples. For example, the Astra Analyzer enables the parallel analysis of samples using incompatible reagents that could not be used in a flow analysis module. On the other hand, the E4A Analyzer provides simplified fluid handling and minimizes reagent consumption. Although it would be desirable to combine such analytical modules and the flow analysis technology, the shear valve of the E4A Analyzer allows only for vertical displacement of the probe. The probe cannot be removed from the shear valve. Also, the shear valve includes a seal around the probe and a seal between the bottom and stationary portions of the valve, both of which are subject to wear during operating cycles of the E4A Analyzer.
Thus, while it is desirable to combine the analysis module and flow analysis technologies, the sample withdrawal, injection and dilution required for the flow analysis technology has been incompatible with the sample probe pickup and horizontal movement required to provide sample volumes to separate analysis modules.